Ke=1/2 M V^2 Not relativistic. So wildly low. But certainly a low bound. My point being that nuclear bomb grade energy is certainly in the ballpark.

By my back-of-the -envelope math it is 4,500,000,000 joules. The Hiroshima bomb is listed at approximately 10,000,000,000,000 joules. I bet xkcd is far more accurate, though.